1. Field of the Invention
This invention relates generally to a shaker table assembly to which manufactured products are mounted for vibrational testing and, more particularly, it relates to a shaker table assembly for a test chamber which increases the low frequency response of the shaker table assembly during vibrational testing of the products.
2. Description of the Prior Art
Shaker tables for testing the reliability and durability of manufactured products are well known in the art. Such shaker tables are used either under controlled laboratory conditions or in conjunction with an assembly line. Often, shaker tables are mounted with thermal chambers, which gives the added flexibility of testing for defects in the manufactured product which can be exposed by elevated temperature or temperature cycling.
The shaker tables typically include a two-piece platform or mounting table having a top piece upon which a product to be tested is mounted and a bottom piece secured to the top piece by bonding or mechanical fasteners. At least one vibrator assembly is typically attached to the bottom piece of the mounting table by a mounting bolt and vibrates the mounting table thereby vibrating the product mounted upon the mounting table. The vibrator assembly generally consists of a housing having a slidable piston mounted therein. The slidable piston strikes a programmer comprising a shock absorbing material to achieve a predicted predetermined shock response. An accelerometer(s) mounted to the bottom piece measures the acceleration level of the mounting table in one or all orthogonal directions, e.g., the x-axis direction (in plane), the y-axis direction (in plane), and the z-axis direction (out of plane).
When testing products with a shaker table in a test chamber, it is important to maximize the acceleration level of the shaker table in all directions, e.g., the x-axis direction, the y-axis direction, and the z-axis direction, in the low frequency range, e.g., between approximately ten (10 Hz) Hertz and approximately two-hundred (200 Hz) Hertz, between approximately ten (10 Hz) Hertz and approximately one thousand (1000 Hz) Hertz, etc. Unfortunately, with the conventional shaker tables of the prior art, maximization of the acceleration level in the low frequency range is poor. In fact, the z-axis acceleration is typically low even though the z-axis acceleration is generally much greater than the acceleration along the x-axis and the y-axis.
Furthermore, it is important to measure the acceleration levels of the top plate of the mounting table since the product is mounted to the top plate. Having the accelerometer mounted to the bottom plate does not always provide an accurate measurement of the acceleration levels of the top plate. Additionally, if the accelerometer is mounted to the top plate on the same side as the product, the accelerometer is prone to damage from the operator of the test chamber during loading, testing, and unloading of the product.
A need exists for a shaker table assembly for a test chamber which maximizes the acceleration level of the shaker table in all directions, e.g., the x-axis direction, the y-axis, and the z-axis direction. Furthermore, there exists a need for a shaker table assembly for a test chamber which allows an accelerometer to be mounted to the top plate of a shaker table assembly for providing accurate measurements of the acceleration levels of the top plate. Additionally, a need exists for a shaker table assembly for a test chamber which insulates and isolates the vibrator assemblies and other components from the thermal environment within the test chamber.